Process for electroslag remelting in a funnel shaped crucible

ABSTRACT

A process for the electroslag remelting of electrodes into ingots, in which a funnel-shaped crucible is continuously moved relative to the ingot during the formation of the ingot. The relative motion between the crucible and ingot exceeds the growth rate of the ingot during at least the largest proportion of the remelting process. The ratio of the diameter of the electrode to the diameter of the ingot is at least greater than one.

[4 1 Oct. 28, 1975 United States Patent 1191 Ellebrecht et al.

[ 1' PROCESS FOR ELECTROSLAG [56] References Cited UNITED STATES PATENTS 164/52 Paton et 164/52 Hopkins..............................

a 523 477 999 111 Ill 1171 336 227 773 67 233 Karl-Georg Redel, Rodenbach, both of Germ any Primary ExaminerFrancis S. Husar Asslgneei Leybold'flel'aells-Gmbfl & C0; Assistant ExaminerJohn E. Roethel Cologne, Germany Attorney, Agent, or Firm.loseph F. Padlon [57] ABSTRACT A process for the electroslag remelting of electrodes 7 [22] Filed: May 16, 1974 Appl. No.: 470,393

into ingots, in which a funnel-shaped crucible is continuously moved relative to the ingot during the for- [30] Foreign Application Priority Data June 6, 1973 mation of the ingot. The relative motion between the crucible and ingot exceeds the growth rate of the ingot during at least the largest proportion of the remelting process. The ratio of the diameter of the electrode to the diameter of the ingot is at least greater than one.

Germany.......... 2328804 52 us. c1. 51 Int. 1

4 Claims, 1 Drawing Figure PROCESS FOR ELECTROSLAG REMELTING IN A FUNNEL SHAPED CRUCIBLE BACKGROUND OF THE INVENTION The present invention concerns a process for the electroslag remelting of electrodes into ingots, preferably witha relationship of diameters of, electrode/ingot, greater than 1. The method uses a funnel-shaped crucible with a substantially cylindrical extension at the lower end, in which during the formation of the ingot, acontinuous relative motion is maintained between ingot and crucible.

From the book by B. E. Paton, Electroslag Welding", 1957 edition, pp. 118 121 and 163 166, it is known'that the position of the melted pool surface should be kept as constant as possible with respect to the guide shoe, which has the function of a crucible or vessel. Paton also states that the measures taken for welding are transferable to block casting.

The principle of constant melted pool surface inside the crucible has previously also been applied in practice to block casting with relative motion between the crucible and the block. A variation of the process is also known, in which a periodic relativemotion between crucible and block is carried out. However, here the locations of the upper and lower points of reversal of the part that is moving with respect to the crucible are constant. The constant position of the surface of the melted pool has previously been accepted also for melting in funnel-shaped crucibles.

With melting in funnel-shaped crucibles, it was found that thesurface of the block exhibits slag inclusions and/or so called metal spills, whichstrongly degrade the quality of the block surface. These arise when the speed of formation of the block even temporarily is greater than the descending velocity of the block or the speed of the crucible. In use of a funnel-shaped crucible, the reason for this can be seen in that the slag skin is held closely to those walls of the crucible that are not vertical. With the required relative motion between block and crucible, the skinof the slag must necessarily tear. If this occurs above the melted pool, then slag runs into the circular crack between the hollow space and the crucible, and forms there a new skin. If the tearing occurs below the pool, then there is the possibility of an outflow of metal, leading to the formation of rag-like protrusions from the block. The influence of block lowering carried out at large intervals of time on the quality of the block surface is greater, the longer the intervals.

' achieved as smooth as possible and as free from slag inclusions and metal spills as possible.

Another object of the present invention is to avoid reworking of the block to remove any metal scrap,

which would be necessary before the block can be machinedg 1 SUMMARY OF THE INVENTION The objects of the present invention are achieved by crucible exceeds the growth rate of the ingot, at least during the greatest part of the melting process. By applying'this condition, the desired goal is fully achieved:

a block is produced with a smooth surface, free from providing that the relative speed between ing'ot and slag inclusions, slag additions, and metal spills. As a reason for this surprisingly appearing success can be given the feature that the fundamentally inevitable tearing of the slag occurs at such small intervals and in such small lengths that one can speak of a quasicontinuous process. To follow the instructions, according to the invention, it is required that the moving velocity of the crucible exceeds the growth rate of the stationary block, or that the descending speed of the block exceed its growth rate within a stationary crucible. This measure leads to the fact that the melted pool, at the beginning of the melting process, is located at the upper end of the cylindrical extension, and moves, during the on-going remelting process, in the direction of the lower end of the crucible. Such a process limits the length of blocks that can be produced. It is, however, possible, by choosing a sufficiently long cylindrical extension of the crucible, to produce blocks of a length of several meters.

It has been proven useful in practice to choose the relative speed between ingot and crucible as l to 15% greater, preferably as between 2 and 5% greater, than the growth rate of the ingot.

The control of the relative speed between ingot and crucible, and particularly the, descending speed of the melted pool in relation to the crucible during the process of formation of the block, can be achieved in the simplest manner indirectly, by providing that the position of the slag pool surface in the crucible is continuously sensed. The relative speed between crucible and ingot is so adjusted, that the slag pool surface continuously descends slightly. Of course, visual control of the slag pool surface in the crucible and manual adjustment of the descending speed of the block or speed of the crucible can be employed with known measuring instruments. This can be done, for example, by continuous measurement of the position of the metal pool surface in the crucible and corresponding regulating facilities. The position of the metal pool surface can be determined by sensing the temperature profile in the crucible by a probe dipped into the slag, by ultrasonics and the like.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING An elevational view with partial section through an electroslag remelting facility, in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawing, in accordance with the present invention, a vertical guide column 10 is attached by means of a base plate 11 to a pedestal 12. A guide shell 13 is movable in vertical direction along guide column 10, and can also rotate horizontally. An electrode-carrying arm 14 is attached to the guide shell. The' free end of the electrode-carrying arm carries a mounting head 15, holding the stub 16 of a meltable electrode 17 in such a way, that, in addition to the mechanical holding action, a reliable electrical current connection is established. Movement of guide shell 13 is accomplished by a regulated drive, not shown in thedrawing.

On guide column there is also another guide shell 18, similarly movable vertically and rotatable horizontally. Guide shell 18' carries crucible-carrying arm 19, at the end of which there is a crucible 20, made in the form of a funnel. Crucible 20 consists of an upper cylindrical part 21 and a narrower lower cylindrical part 22, between which there is a conical transitional part 23. Parts 21 23 constitute a unit, which encloses a common hollowspace, through which flows a cooling liquid.

The facility is shown at a stage, at which a portion of the meltable electrode 17 has already been'melted into an ingot 24 being built up. The ingot 24 rests on a raisable and lowerable platform 25, connected by column 26 to a drive, not shown. The moving velocities of the guide'shell 13, the guide shell 18, and the column 26 are so adjusted relative to one another as to preserve the relative orientation of the parts shown in the drawfixed in place and to raise crucible 20 in the manner taught by the invention. On the other hand, it is also possible to'fix crucible 20 in place and to lower platii g into the upper cylindrical part 21 of the crucible,

and is in electrically-conducting contact with meltable electrode 17 to form a'current path. Below slag layer 27 there is a melted pool 28, out of which ingot 24'is forrr ied byprogress'ive'crystallization. At the beginning of theactual remelting process, the upper surface of melted pool 28 is in the position designatedhj Because of the relative motion according to the invention, the

upper 'surface of the melted pool 28 moves gradually into position 11 in the course of the remelting process.

' The melted pool then assumes the position 28f, shown bydashed lines.'The adjustment of the length of ingot .24' and the length of the lower cylindrical part 22 of crucible 20 has to be such that position 11 of the suryface of the melted pool still lies sufficiently far above thelower edge of the crucible to prevent the formation of spills. ofslag and/or metal melts. The crucible 20,

because of its cooling function, is coated by a solid skin of slag 29 in the region of melted slag 27. The skin is held to the walls because of the conical transition part 23 of crucible 20. During the melting process, the ingot '24 is also coated, with a skin of slag 30. Due to the relative motion between crucible 20 and and ingot 24 with skin of slag 30, a continuous tearing of the skin of slag occurs in the'region of melted pool 28 or 28. The tears are immediately filled and closed by liquid slag. This process should be made as continuous as possible.

. In an exemplary experiment, a facility inaccordance with the drawingwas equipped with a crucible 20, with an uppercylindrical part 21 of diameter 400 mm, a

lowercylindrical part 22 of diameter 150 mm, and a conical transitional part 23 with an angle of 30. The crucible 20 was fixed 'in place, and was closed at the beginning of. the-remelting process by the platform 25. 30 kilograms of powdered slag in the combination of 40% ing. It is of course possible to construct the platform r Cal-" 30% CaO, and 30% A1 05 were introduced into the crucible. At the start, the slag granules came up to approximately the height, of the surface of the melted pool designated as h,. The meltable electrode 17 at first had a thin cylindrical stub on its lower face, reaching down to platform 25, by means of which the slag was melted. At the end of the starting phase, the upper sur face of the slag layer 27 was approximately at the height shown in the drawing. At this instant began the remelting process of the meltableelectrode 17, which consisted of structural steel St. 52-3 and had a diameter of 300 mm. The remelting process was'carried' out with a melting current of 6000 amps. with an average melting voltage of age of volts, resulting in a melting rate of 200 kilograms/hr. A partial length of 150 mm was melted off the meltable electrode 17 d'uringa melting time of 25 minutes. Based on the melting rate and the given cross-section of the lower cylindrical, part 22 a of crucible 2 0, a descending speed of the platform 25 of 24 mm/min. is calculated, on the assumption that the melted pool 28 is held constant at the upper'position. For carrying out the process according to the inven-- tion, however, platform 25 was lowered with an "8% greater speed, so that a speed of 26 mm/min. resulted. With the passage of time, because of the given higher speed, the melted pool sank to the position designated 11 At the end of the remelting process, the melted pool 28 was 5 cm removed from the starting position. The lower cylindrical part 22 had a length of 25 cm. The completed ingot 24 had an overall lengthof 600mm. The surface couldbe very easily cleaned of the slag skin. No slag inclusions or metal spills could be recognized at the surface of the ingot. Control of the descending speed in conjunction with the sensing of the instantaneous position of melted pool 28 was achieved in a known manner, i.e. through, control of the temperature profile in the lower cylindrical part 22 of crucible 20.

Without further analysis, the foregoing will so fully reveal the 'gist of the present invention that others can,

' by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention. I

1,. A process for the electroslag remelting of electrodes into ingots comprising the steps of: moving continuously a funnel-shaped crucible with a substantially cylindrical extension at the lower end thereof relative to the ingot during the formation'of the ingot,'the relative motion between said crucible and said ingot eX-,

ceeding the growth rate of the ingot at least during the largest part of the remelting process, the electrical current taking the shortest paths between said electrode and the inclined walls of said funnel-shaped crucible,

the slag temperature at the top of the crucible being substantially higher than the temperature near the molten pool, the slag being a substantially viscous liquid forming a thick layer of slag on the walls of said crucible and on the surface of the ingot, the continuous motion of said crucible relative to said ingot providing a substantially smooth surface of the ingot."

2. A process as defined in claim 1 wherein the ratio of the diameter of the electrode to the diameter of the ingot is given by: i

range of l% to electrode diameter 4. The process as defined in claim 1 wherein the rela- Z l. mgot mama" tive motion between said crucible and said ingot ex- 3. The process as defined in claim 1 wherein the rela- 5 ceeds the growth rate of said ingot by an amount in the tive motion between said crucible and said ingot exceeds the growth rate of said ingot by an amount in the range of 2% to 

1. A PROCESS FOR THE ELECTROSLAG REMELTING OF ELECTRODES INTO INGOTS COMPRISING THE STEPS OF: MOVING CONTINUOUSLY A FUNNELSHAPED CRUCIBLE WITH A SUBSTANTIALLY CYLINDRICAL EXTENSION AT THE LOWER END THEREOF RELATIVE TO THE INGOT DURING THE FORMATION OF THE INGOT, THE RELATIVE MOTION BETWEEN SAID CRUCIBLE AND SAID INGOT EXCEEDING THE GROWTH RATE OF THE INGOT AT LEAST DURING THE LARGEST PART OF THE REMELTING PROCESS, THE ELECTRICAL CURRENT TAKING THE SHORTEST PATHS BETWEEN SAID ELECTRODE AND THE INCLINED WALLS OF SAID FUNNEL-SHAPED CRUCIBLE, THE SLAG TEMPERATURE AT THE TOP OF THE CRUCIBLE BEING SUBSTANTIALLY HIGHER THAN THE TEMPERATURE NEAR THE MOLTEN POOL, THE SLAG BEING A SUBSTATIALLY VISCOUS LIQUID FORMING A THICK LAYER OF SLAG ON THE WALLS OF SAID CRUCIBLE AND ON THE SURFACE OF THE INGOT, THE CONTINUUS MOTION OF SAID CRUCIBLE RELATIVE TO SAID INGOT PROVIDING A SUBSTANTIALLY SMOOTH SURFACE OF THE INGOT.
 2. A process as defined in claim 1 wherein the ratio of the diameter of the electrode to the diameter of the ingot is given by:
 3. The process as defined in claim 1 wherein the relative motion between said crucible and said ingot exceeds the growth rate of said ingot by an amount in the range of 1% to 15%.
 4. The process as defined in claim 1 wherein the relative motion between said crucible and said ingot exceeds the growth rate of said ingot by an amount in the range of 2% to 5%. 